Why He Minds the Nest While She Takes More Mates

The male wattled jacana tolerates being cuckolded—because there's something in it for him.

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A male wattled jacana, photographed at the Dallas World Aquarium.

Photograph by JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK

This story appears in the
May 2017 issue of
National Geographic magazine.

What kind of dad stays home with the kids while their mother is out having sex? A wattled jacana dad—even when he knows that he’s being cuckolded and the offspring he’s minding may not be his.

Several species of Jacana are among the animal world’s most extreme cases of sex-role reversal, says behavioral ecologist Peter Wrege of Cornell University. An assertive female collects a harem of up to five smaller males. In the span of about a week, she lays four eggs in one male’s nest while continuing to mate openly with him and others—“as many as 65 matings for one clutch,” Wrege says.

Even in monogamous bird species, a female may “sneak copulations elsewhere,” he says. But as Wrege and colleague Stephen Emlen observed during years of research in Panama, the wattled jacana female’s cuckoldry is both public and frequent. To see how that affects paternity of offspring, they tracked dozens of birds’ mating and egg laying, took blood samples, and ran DNA tests.

The researchers concluded that for a jacana male with a promiscuous partner, “the risk of raising unrelated young may be as high as 75 percent.” In other words: He’s seen her mating with others, yet for three months he incubates eggs and raises chicks unlikely to all be his.

Why do the males do this? “Basically, they’re stuck,” Wrege says. Hunting for a less promiscuous female would take time better spent trying to sire eggs. This way, although they may end up with other males’ kids, they also achieve the biological imperative of having their own.